Process for producing n:n&#39;-dilower alkyl-4:4&#39;-bipyridylium salts



US. Cl. 260296 18 Claims ABSTRACT OF THE DISCLOSURE There is provided aprocess for the production of an N:Ndisubstituted 4:4-bipyridylium saltsby the interaction of an N:N-disubstituted tetrahydro-4:4-bipyridyl witha carbon compound containing a labile halogen atom wherein the labilehalogen atom is attached to carbon by a bond of dissociation energy lessthan about 70 kcaL/mole. The process will produce salts which are usefulas herbicides.

This invention relates to the production of bipyridylium salts andparticularly to the production of bis-quaternary salts of 4:4-bipyridyl.

It is known that bis-quaternary salts of 4:4-bipyridyl are usefulherbicides and these compounds are usually made by a quaternisationreaction from 4:4-bipyridyl. It is also known that N:N'-dibenzyltetrahydrobipyridyl can be oxidised to an N:N'-dibenzyl bipyridyliumsalt by the action of iodine, but this process gives only poor yields ofthe bipyridylium salt, and much of the starting material is convertedinto benzyl pyridinium salts by fission of the bond connecting the twopyridine rings.

In UK. applications Nos. 14,720/64 and 36,729/64, certified copy ofwhich is in the file of US. application Ser. No. 445,770, filed on Apr.5, 1965, we have described processes whereby N:N'-disubstitutedtetrahydro-4:4-bipyridyls may be oxidised to N:N-disubstituted-4:4-bipyridylium salts by organic oxidants particularly quinones. We have nowfound that the N:N'-disubstit-utedtetrahydro-4:4-bipyridyls may beconverted in good yield into N:N-disubstituted 4:4-bipyridylium salts bythe action of compounds containing a labile halogen atom.

Thus according to our invention we provide a process for the conversionN:N-disubstituted tetrahydro-4:4'-bipyridyls to N:N'-disubstituted 4:4bipyridylium salts which comprises treating the tetrahydrobipyridyl withone or more carbon compounds which each contains a labile halogen atom.We do not include fluorine in the term halogen atom.

The tetrahydrobipyridyls which may conveniently be used in our processare those more fully described in the above mentioned U.K. applications,for example tetrahydrobipyridyls which carry alkyl or carbamyl alkyl,and particularly methyl or N:N-disubstituted carbamyl methylsubstituents on the nitrogen atoms. Other suitableN:N-disubstituted-tetrahydro-4:4 bipyridyls are those carrying inertsubstituents, for example alkyl groups, on the carbon atoms of thepyridine nuclei.

The carbon compound containing a labile halogen atom may be any suchcompound which is capable of nited States Patent 3,461,128 Patented Aug.12, 1969 removing hydrogen from the tetrahydrobipyridyl, for example acompound containing a carbon-to-halogen bond of dissociation energy lessthan about kcals./mole. Such carbon compounds include those in which thehalogen is attached to an electron withdrawing group for example a CHal(where Hal=Cl, Br or 1), CO, F, Br or Cl group. We have found that it isconvenient to use liquid or solid carbon compounds and particularlyliquid or solid compounds containing less than 4 carbon atoms permolecule. Bromine and iodine atoms tend to be more labile than chlorineatoms when attached to carbon and compounds containing bromine andiodine will therefore tend to be more effective than those containingchlorine only. However compounds containing bromine and iodine arerelatively expensive and it is therefore economically desirable to usethe cheaper compounds containing chlorine. We also prefer to use highlyhalogenated compounds and in particular fully halogenated compounds suchas carbon tetrahalides (other than carbon tetrafiuoride). In particularthere may be used a carbon tetrahalide which does not contain fluorine,for example carbon tetrachloride, carbon tetrabromide,bromotrichloromethane or dichlorodibromo m e t h a n e. Other compoundswhich may be used in our invention are bromoform, iodoform, methyleneiodide, hexachloroethane, hexachloropropene, 1:1:1 trifiuoro 2:2dibromo-Z-chloroethane and hexachloroacetone. We have found that use ofchloroform, methylene dichloride, benzotrichloride and monochlorobenzenetends to yield very little of the desired product.

The tetrahydrobipyridyl and the carbon compound containing the labilehalogen atom may be interacted simply by mixing the two components, butthis procedure tends to give rise to a vigorous reaction which may bedifficult to control. We have therefore found it useful to moderate thisreaction by carrying it out in solution in an inert solvent. Suitablesolvents are those which will dissolve theN:N'-disubstituted-tetrahydro4:4-bipyridyl and also the carbon compoundcontaining the labile halogen atom. Examples of such solvents are ethersfor example diethyl ether, tetrahydrofuran, 1:2 dimethoxyethane, bis (2-methoxyethyl) ether and 1:4-dioxane; ketones, for example acetone;hydrocarbons, for example benzene and hexane; organic bases, for examplepyridine; halogenated hydrocarbons, other than those used to interactwith the tetrahydrobipyridyl, particularly chlorinated hydrocarbons, forexample chlorobenzene, chloroform and methylene dichloride; amides,particularly tertiary alkylamides, for example formamide; sulphoxides,for example dimethyl sulphoxide or nitriles, for example acetonitrile.We prefer that the tetrahydrobipyridyl and the carbon compoundcontaining a labile halogen atom be dissolved in the same solvent asthis avoids difficulties inherent in the use of mixed solvents.

The concentration of the tetrahydrobipyridyl may conveniently be aboveabout 0.75 mole per litre and the concentration of the carbon compoundcontaining a labile halogen atom, for example carbon tetrachloride, maybe above about 0.25 mole per litre. Lower concentrations of eitherreagent necessitates the recovery of the N:N-disubstituted bipyridyliumsalts from large quantities of solvent and therefore tend to beinconvenient. Either reagent may if desired be used undiluted, the otherreagent being dissolved in the chosen solvent, but if the reagents are Qused in high concentration care should be taken that the reaction doesnot become too vigorous and lead to some destruction of the desiredproduct or to the production of unwanted by-products.

halogen atom, the solvent, the concentration of the reagents in thesolvent, the reaction temperature and the time of the reaction. Thesevariations and their effects on the yield of bipyridylium saltscalculated on the tetra- We prefer to use such a proportion of carboncom- 5 hydrobipyridyl used are set out in the following table.

TABLE Carbon Compound (A) eon- Volume of tetra- Yield of bipyritammg alabile halogen Weight of (A) Volume of (A) hydrobipyridyl Temperature,Reaction time, dylium salt, per

atom gms. Solvent solution, ml. solution, ml. 0. hrs. cent of theory 27Diethyl other. 600 450 55 24 79 Dibutyl car tol 100 100 35 24 17 Dicthylother 100 100 35 14 16 Hexachloroethane 200 200 35 1 :21

Methylene iodide 200 200 35 1 13 Carbon tetrabromide 200 200 35 1 22Hexachloropropene. 450 600 20 1. 30

Hexachloroaeetone 450 200 25 0. 5 14 Bromolorm 450 200 25 1 11CF3CBI'201 250 600 35 1 Ildol'orm 500 500 35 1 17 pound containing alabile halogen atom that two labile halogen atoms are available for eachmolecule of tetrahydrobipyridyl; thus about, or rather more than, 2moles of a carbon compound containing one labile halogen atom permolecule should be used to interact with 1 mole of tetrahydrobipyridyl.A smaller proportion of carbon compound containing a labile halogen atomwill tend to leave some of the tetrahydrobipyridyl unreacted and alarger proportion will leave an excess of the halogen containing carboncompound.

The temperature at which reaction is carried out will depend on theconcentration of the reagents and on the particular reagents used. Wehave found that suitable temperatures are from about 55 C. to 70 C. andpreferably from 0 C. to 50 C.; higher temperatures tend to causedecomposition of the tetrahydrobipyridyls and lower temperatures willnecessitate cooling of the reactants. The most suitable time of reactioncan be found by simple experiment and will depend on the reagents usedand the temperature at which the reaction is earned out; we have howeverfound that a minimum time of 20 to 30 minutes is generally necessary.The mechanism of the reaction is at present obscure but it appears thatthe labile halogen atom from the carbon compound is replaced by one ofthe hydrogen atoms from the tetrahydrob1pyr1dyl. Thus when carbontetrachloride is used in the reaction chloroform as well as theN:N-disubstituted bipyridylium salt is found in the reaction product.

The N:N-disubstituted bipyridylium salt may be recovered from thereaction mixture by conventional processes for example by extraction ofthe reaction mixture with water or with a dilute aqueous solution of amineral acid such as sulphuric, hydrochloric or phosphoric acid. TheN:N-bipyridylium salt may then be recovered from the aqueous phase,which has previously been separated from the organic phase, byevaporation of the water and crystallisation of the salt.

The invention is illustrated but not limited by the following example inwhich the parts and percentages are by weight.

EXAMPLE A solution of 1:1 dimethyl-1:1:4:4-tetrahydrobipyridyl (16.55gms.) in an inert solvent was mixed with a solution of a carbon compoundcontaining a labile halogen atom in the same solvent. The mixture washeated to the required temperature and maintained at the temperature fora given time. The mixture was then treated with aqueous hydrochloricacid (7.3 gms. in 200 mls.), and the aqueous phase separated andanalysed polarographically for N:N-dimethyl-4:4'-dipyridylium salts. Theprocedure set out above was repeated, variations being made in thecarbon compound containing a labile What we claim is:

1. A process for the production of an N:N-dilower alkyl-4:4-bipyridyliumsalt which comprises reacting in an inert solvent a N:N-dilower alkyltetrahydro-4:4-bipyridyl with a linear alkyl or linear alkenyl carboncompound having less than 4 carbon atoms and containing a labile halogenatom selected from chlorine, bromine and iodine and the labile halogenatom is attached to carbon by a bond of dissociation energy less thanabout 70 kcal./mole.

2. A process as claimed in claim 1 wherein the labile halogen atom isattached to a carbon atom which is attached to an electron Withdrawinggroup.

3. A process as claimed in claim 2 wherein the electron withdrawinggroup is a carbonyl group, a CHal group (where Hal represents chlorine,bromine or iodine), or a fluorine, chlorine or bromine atom.

4. A process as claimed in claim 1 wherein the labile halogen atom ischlorine.

5. A process as claimed in claim 1 wherein the carbon compound is fullyhalogenated.

6. A process as claimed in claim 1 wherein the carbon compound is acarbon tetrahalide not containing fluorine.

7. A process as claimed in claim 6 wherein the carbon tetrahalide iscarbon tetrachloride or carbon tetrabromide.

8. A process as claimed in claim 1 wherein the carbon compound isbromotrichloromethane, dichlorodibromomethane, bromoform, iododform,methylene iodide, hexachloropropene, hexachloroacetone or1:1:1-trifiuoro-2:2- dibromo-Z-chloroethane.

9. A process as claimed in claim 1 wherein the interaction of thetetrahydrobipyridyl and the carbon compound containing a labile halogenatom is carried out in an inert solvent.

10. A process as claimed in claim 9 wherein the solvent comprises anether.

11. A process as claimed in claim 10 wherein the ether is diethyl ether,tetrahydrofuran or bis-(Z-methoxy ethyl) ether.

12. A process as claimed in claim 9 wherein the solvent comprisesdiethyl ether, tetrayhdrofuran, 1:2-dimethoxyethane,bis-(Z-methoxyethyl) ether, 1:4-dioxane, acetone, benzene, hexane,pyridine, chlorobenzene, chloroform, methylene dichloride, formamide,dimethyl sulphoxide and acetonitrile.

13. A process as claimed in claim 9 wherein the initial concentration oftetrahydrobipyridyl in the reaction mixture is more than about 0.75 moleper litre.

14. A process as claimed in claim 9 wherein the initial concentration ofcarbon compound in the reaction mixture is more than about 0.25 mole perlitre.

15. A process as claimed in claim 1 wherein the pro- 3,461,128 5 6portion of carbon compound used is such that substanpyridyliurn salt isextracted from the reaction mixture by tially two labile halogen atomsare available for each water. molecule of tetrahydrobipyridyl.References Cited 16. A process as claimed in claim 1 wherein the inter-UNITED STATES PATENTS action is carried out at a temperature in therange 55 C to C 5 3,227,723 1/1966 Baines e1: a1. 260-296 17. A processas claimed in claim 1 wherein the inter- 3272835 9/1966 Dransfi 61d et260296 action is carried out at a temperature in the range of 0 HENRY R.JILES Primary Examiner C. to 50 C.

18. A process as claimed in claim 1 wherein the bi- 10 ALAN ROTMANIAssistant Examiner

